Optical mark scanning apparatus (hereinafter referred to as optical mark reading or OMR systems) are well known in the prior art. There are a wide variety of applications that use OMR systems and scannable forms in the large-scale gathering of discrete pieces of information recorded on documents (e.g., scores from standardized tests, census information, preference surveys, etc.). OMR systems generally sense data recorded with marks containing pigment that absorbs light in the near infrared range (e.g., No. 2 pencil mark) specific, predefined fields on a form. (This is called NIR-mode scannig.) Such data are position-encoded, in that their meaning is interpreted based on where the data has been marked on the form document used to record it. A primary advantage of NIR-mode scanning is that it allows separation of the respondent-marked variable data from the standard background printing on the same document.
Although a more recent development, visual image scanning apparatus (hereinafter referred to as VIS mode scanners or VIS systems) are also well known in the prior art. Most of the applications for current VIS systems have developed out of the desire to find replacements for traditional microfilm image capture systems. As a result, the focus of current VIS systems is on the acquisition of the total scanned image of a document, as compared to the detection, dark mark resolution and processing of discrete pieces of information recorded in predefined fields done by current OMR systems.
One of the limitations with current OMR systems that focus on predefined fields is their lack of any ability to scan or reproduce the context of a scannable form surrounding the predefined fields. As a result, the retrieval and viewing or hard copy replication of the stored or archived discrete, raw information from a form scanned by an OMR system is of limited value, because there is no capability for interpreting that information without resorting to the form, a transparent overlay, or even a booklet associated with the form, as is the case in standardized testing.
VIS systems, on the other hand, are capable of reproducing the entire contents of a scannable form (both standard background printing and any variable data) as a digitized, pixel image, but any associated OMR processing logic cannot easily interpret or analyze any of the discrete, variable information contained in a VIS-mode pixel image of the form. A great deal of digitized data, both fixed and variable, can be collected by VIS images, but the meaning of the variable data remains to be extracted and not all of the VIS-mode data collected may be of interest. For example, if an 81/2".times.11" piece of paper is scanned at a resolution of 120 dots per inch (DPI), vertically and horizontally, and with an eight-bit grayscale, more than 1.3 megabytes worth of bit-level scanned information may be generated from this single page. Obviously, a tremendous amount of computer processing power may be necessary to extract and analyze significant bit-level information representing the variable data or localized pixel segments (often called areas of interest or AOI's ) from a form scanned with a VIS system. More importantly, the storage requirements for storing all of this information in a situation where hundreds or thousands of documents are being processed to capture a complete pixel image as a by-product of capturing the variable data is so large as to be prohibitively expensive in most applications. When data are recorded on standard forms, much of the data collected in a VIS system is redundant. What is needed is a scanning system and method that permits repeated data on standard forms to be scanned and stored once, while variable data, such as pencil marked test answers, signatures, other respondent-marked data, are scanned and stored at every occurrence and that permits the relationship between variable data and repeated data to be recovered.